This application is a 371 of PCT/EP99/06589 filed Sep. 7, 1999.
The present invention relates to a novel process for the synthesis of olefins having aromatic substituents using a very simple catalyst system.
In industrial chemistry, olefins having aromatic substituents play an important role, e.g., as starting materials for sunscreen agents, polymers, fine chemicals and active substance precursors for pharmaceuticals, plant-protection agents and perfumes.
One possibility for the synthesis of aryl-substituted olefins is the so-called Heck reaction in which iodo-, bromo- or chloroaromatics ArX (X=I, Br, Cl) are reacted with olefins in the presence of stoichiometric amounts of a base and catalytic amounts of a palladium compound, such as Pd(PPh3)4 (R. F. Heck, xe2x80x9cVinyl Substitutions with Organopalladium Intermediatesxe2x80x9d in Comprehensive Organic Syntheses, Vol. 4, Pergamon Press, Oxford, 1991, p. 833; R. F. Heck, Palladium Reagents in Organic Syntheses, Academic Press, London, 1985; R. F. Heck, Org. React. (N.Y.) 1982, 27, 345; A. de Meijere, F. E. Meier, Angew. Chem. 1994, 106, 2473; J. Tsuji, Palladium Reagents and Catalysts: Innovations in Organic Synthesis, Wiley, Chichester, 1995). In some cases, triflates ArOTf or diazonium salts ArN2+Xxe2x88x92 may also be employed (see the above references). 
Despite the many publications from university laboratories, the Heck reaction has been used virtually not at all for industrial application to date. This is due to the fact, inter alia, that the reactivity of haloaromatics ArX decreases fast in the order ArI greater than ArBr greater than ArCl. Thus, the iodides ArI are mostly employed under relatively mild conditions (80-110xc2x0 C.). However, such substrates are very expensive. In the case of bromoaromatics, the common catalysts or precatalysts, such as Pd(PPh3)4, Pd(OAc)2, in the presence of excess PPh3 or P(tolyl)3, result in acceptable yields at reaction temperatures of about 140xc2x0 C. However, drawbacks include the high amounts of palladium required (1-2 mole percent) and the fact that phosphanes are needed. Therefore, there have been many attempts to develop phosphane-free catalyst systems for Heck reactions. However, despite of a certain progress (A. S. Carlstroem, T. Frejd, J. Org. Chem. 1991, 56, 1289-1293; S. Sengupta, S. Bhattacharya, J. Chem. Soc. Perkin Trans I 1993, 1943-1944; N. A. Bumagin, V. V. Bykov, I. P. Beletskaya, Russ. J. Org. Chem. 1995, 31, 439-444; M. S. Stephan, A. J. J. M. Teunissen, G. K. M. Verzijl, J. G. de Vries, Angew. Chem. 1998, 110, 688-690; Angew. Chem. Int. Ed. Engl. 1998, 37, 662-664; A. F. Shmidt, A. Khalaika, D. -H. Li, Kinet. Catal. 1998, 39, 320; R. Gauler, N. Risch, Eur. J. Org. Chem. 1998, 1193-1200; S. Brxc3xa4se, J. Rxc3xcmper, K. Voigt, S. Albecq, G. Thurau, R. Villard, B. Waegell, A. de Meijere, Eur. J. Org. Chem. 1998, 671-678; L. F. Tietze, R. Ferraccioli, Synlett 1998, 145-146; R. L. Augustine, S. T. O""Leary, J. Mol. Catal. A: Chemical 1995, 95, 277-285; M. Beller, K. Kxc3xcchlein, Synlett 1995, 441-442; S. Sengupta, S. Bhattacharya, J. Chem. Soc. Perkin Trans I 1993, 1943-1944; J. Kiviaho, T. Hanaoka, Y. Kubota, Y. Sugi, J. Mol. Catal. A: Chemical 1995, 101, 25-31), a satisfactory or general catalyst system could not be found. Therefore, more recent works using so-called palladacycles have attracted attention (W. A. Herrmann, C. Brossmer, K. xc3x96fele, C.-P. Reisinger, T. Priermeier, M. Beller, H. Fischer, Angew. Chem. 1995, 107, 1989-1992; Angew. Chem. Int. Ed. Engl. 1995, 34, 1844; W. A. Herrmann, C. Brossmer, C.-P. Reisinger, T. H. Riermeier, K. xc3x96fele, M. Beller, Chem. -Eur. J. 1997, 3, 1357-1364; M. Ohff, A. Ohff, M. E. van der Boom, D. Milstein, J. Am. Chem. Soc. 1997, 119, 11687-11688; DE 44 21 730 C1; EP 0 725 049 A1). Actually, bromoaromatics can be converted smoothly, even with only 0.01 mole percent of palladacycle. However, such catalysts are expensive or require several synthetic steps using the expensive tris(o-tolyl)phosphane or other phosphanes which are difficult to obtain. In the case of certain chloroaromatics, an active catalyst system consisting of PdCl2(PhCN)2, Ph4P+Clxe2x88x92 and N,N-dimethylglycine (DMG) as an additive was recently described; in the absence of the phosphonium salt Ph4P+Clxe2x88x92, no reaction occurs (M. T. Reetz, G. Lohmer, R. Schwickardi, Angew. Chem. 1998, 110, 492-495; Angew. Chem. Int. Ed. Engl. 1998, 37, 481-483; M. T. Reetz, G. Lohmer, R. Schwickardi DE-A 197 12 388.0, 1997). However, this catalyst system is less suitable for bromoaromatics. Further, phosphonium salts are required, which in turn necessitate the use of phosphanes.
Surprisingly, it has now been found that a strikingly simple, inexpensive and phosphane-free catalyst system causes smooth Heck reactions of bromoaromatics, even when low quantities of the catalyst or precatalyst are employed. The novel catalyst system consists of inexpensive palladium(II) salts in the presence of nitrogen-containing additives, such as N,N-dimethylglycine (DMG), and a base. Thus, the use of phosphanes can be dispensed with.
In addition, it was found that, when very low quantities of simple palladium salts are used, the reaction also proceeds without an additive, though with significantly increased reaction times. Only at concentrations of more than 0.5 mole percent of palladium, the additive has a highly accelerating effect.
As catalysts, there are used common palladium(II) salts PdXY or their CH3CN or PhCN complexes, wherein typically X=Y=Cl, Br, I, NO2, RCO2 [R=C1-C22, CF3, CCl3, CH2N(CH3)2, C6H5] or RSO3 (R=C1-C22, CF3, C4F9, CCl3, C6H5, p-CH3C6H4), or typically X=Cl, Br, I, RCO2 (R=C1-C22, CF3, CCl3, CH2OCH3, C6H5) and typically Y=C6H5, o-, m-, p-CH3C6H4, o-, m-, p-Cl-C6H4, o-, m-, p-CHOC6H4, o-, m-, p-CN-C6H4, o-, m-, p-NO2-C6H4, o-, m-, p-PhCO-C6H4, o-, m-, p-F-C6H4, 1-C10H7 or 2-C10H7. Preferably, Pd(OAc)2, PdCl2(PhCN)2, PdCl2, PdCl2(CH3CN)2, C6H5PdCl or Pd(NO3)2 or their dimeric or oligomeric forms are used.
As additives, there are used nitrogen-containing carboxylic acids, such as common xcex1- or xcex2-amino acids H2N(R)CHCO2H or H2N(R)CHCH2CO2H [R=H, CH3, C6H5, CH2C6H4, CH(CH3)2], or their N-alkylated forms Rxe2x80x2NH(R)CHCO2H or Rxe2x80x2NH(R)CHCH2CO2H, or Rxe2x80x22N(R)CHCO2H or Rxe2x80x22N(R)CHCH2CO2H [Rxe2x80x2=CH3, C2H5, C3H7, C4H9, or Rxe2x80x2+Rxe2x80x2=(CH2)4 or (CH2)5], or their sodium or potassium salts, anthranilic acid or N,N-dimethylanthranilic acid, or pyridinecarboxylic acids (or their sodium or potassium salts), such as 2-pyridinecarboxylic acid, or aromatic nitrogen-containing heterocycles, such as 2,2xe2x80x2-dipyridyl. Preferably, N,N-di-methylglycine is used. The ratio of additive to palladium ranges between 100:1 and 1:1, preferably between 50:1 and 1:1.
The use of these additives has the effect that the reaction time and reaction temperature can be significantly decreased. Further, such substances increase the selectivity of the reaction.
Aprotic dipolar solvents, such as dimethylformamide (DMF), dimethylacetamide (DMA), dimethyl sulfoxide, propylene carbonate, 1,3-dimethyl-3,4,5,6-tetra-hydro-2(1H)-pyrimidinone (DMPU) or 1-methyl-2-pyrrolidinone (NMP), but also protic solvents, such as methanol, ethanol or diethylene glycol, are used as the solvents. Preferably, DMF, NMP or methanol is used.
Metal salts, such as sodium, potassium, cesium, calcium or magnesium salts of carboxylic acids, or the corresponding carbonates or bicarbonates, or amines, such as triethylamine or trioctylamine, preferably sodium acetate, are used as the base. The ratio of base to aryl halide ranges between 1:1 and 5:1, preferably 1.5:1 to 2:1.
Reaction temperatures of between 60xc2x0 C. and 180xc2x0 C. may be selected; preferably, the reactions are allowed to proceed between 100xc2x0 C. and 140xc2x0 C.
As to the aryl component ArX, a wide variety of aryl and heteroaryl halides, preferably aryl bromides, but also -O-tosylates, -O-mesylates or -O-triflates may be employed, for example, benzene, naphthalene, pyridine or quinoline derivatives. Aryl diazonium salts may also be reacted.
In the olefin component of the above formula II, R1, R2 and R3 are independently hydrogen, alkyl-(C1-C8), phenyl, 1- or 2-naphthyl, vinyl, O-alkyl-(C1-C8), O-phenyl, CN, CO2H, CO2-alkyl-(C1-C8), CO2-phenyl, CONH2, CONH-alkyl-(C1-C5), CON(alkyl)2-(C1-C5), fluoro, chloro, PO(phenyl)2, PO(alkyl)2-(C1-C5), CO-phenyl, CO-alkyl-(C1-C5), NH-alkyl-(C1-C4), SO3H, PO3H, SO3-alkyl-(C1-C4) or SO2-alkyl-(C1-C4); further, cyclic derivatives are also possible, namely if R1+R2=(CH2)n or R2+R3=(CH2)n, wherein n may be from 2 to 16.